Unfortunately, she was competing at the Olympic Aquatics Stadium.
The transportation mix-up left officials scrambling to make sure Halsall and two other swimmers got a chance to compete in the semifinals of the women's 50-meter freestyle Friday night.
"The whole Olympics had to be stopped for me tonight, unfortunately," Halsall told the BBC.
Two hours before the race, she boarded a bus at the Olympic village along with fellow semifinalists Jeanette Ottesen of Denmark and Aliaksandra Herasimenia of Belarus.
They thought it was taking them to the nearby swimming stadium. Instead, it headed to the stadium used for the athletics competition, the driver apparently failing to heed the protests of the swimmers who wanted to go to the pool.
"It took us to the Olympic Stadium, which happens to be 40 minutes in the opposite direction to the pool," Halsall said. "So I ended up going and having a nice tour around the Olympic Stadium, 40 minutes back to the village and then back to the pool for warmups. My emotions and adrenaline were all over the place."
At the pool, officials were informed of the problem and altered the night's schedule, moving a pair of medal ceremonies ahead of the 50 free semifinals to give the wayward swimmers a little extra time to prepare. An announcement was made to the crowd at the start of the competition, but no reason was given for the change.
Halsall still managed to qualify for Saturday's final with the fourth-fastest time, and Herasimenia also advanced in the last of eight spots. Ottesen was eliminated.
"If I get on the right bus tomorrow, everything will be good," Halsall quipped to the BBC.